I would like to know if there is any guidance about how many wizards of what levels exist in various campaign settings. I'm particularly interested in the Forgotten Realms and in Eberron, since these are the two settings that I think of as "high magic", and for that and other reasons are the closest comparisons to my own CW of Whiteleaf, which is deliberately designed to be a "high magic" world in a different sense than both of them. The vague feeling I have, from looking at material related to both settings, is that Eberron has a lot of low-level magic users (particularly the NPC "magewrights" rather than wizards per se), making it a world in which petty forms of magic are commonplace, but that there aren't very many high-level mages who move and shake the world. Meanwhile, FR seems to be the exact opposite, a medieval setting that's so primitive that most people still use outhouses and chamber pots, but where every third village has one eccentric old resident who's secretly a 20th-level evoker or a polymorphed dragon, who in either case is perfectly capable of casting a 9th-level spell whenever they feel like doing so, and thus could effortlessly solve all manner of geopolitical issues if they ever wanted to bother.
If these impressions are accurate, I'd like to see some numbers codifying them, so that I could then modify those numbers for use in my Whiteleaf worldbuilding. My objective is to have that world contain more low-level casters than Faerun but fewer than Eberron, and the reverse for the high end. I don't want a full-blown Tippyverse, and I want to steer clear of both the relative mundanity of magecraft on Eberron as well as the "Elminster syndrome" of FR, but I do want to be significantly more in both of those directions than a grittier-feeling setting such as Greyhawk or Birthright (or for that matter Planescape). Whiteleaf needs to have enough casters that ordinary life can be improved in various significant ways, helping the population to be relatively comfortable and more easily uplifted than downtrodden, while still having to work for what they value in life instead of just having things handled for them by greater forces. There should be very few NPCs with godlike power that they can effortlessly use in six seconds to wipe out an entire army, but there should also be enough of them that the entire planet is not routinely threatened with annihilation. I'm going for a sort of "cold war between Good and Evil" vibe, where problems are usually solved with spycraft rather than brute force, and looking to construct mechanics that will support this; a population demographics chart by PC and NPC class would be one such useful feature, but I'm not knowledgeable enough to create it without some reference material from past eras.